Method and apparatus for polishing semiconductor wafers

ABSTRACT

A system and method for planarizing a plurality of semiconductor wafers is provided. The method includes the steps of processing each wafer along the same process path using at least two polishing stations to each partially planarize the wafers. The system includes an improved process path exchanging a detachable wafer carrying head with spindles at each processing point and conveying the detached wafer carrying heads in a rotary index table between processing points. The system also provides for improved polishing accuracy using linear polishers having pneumatically adjustable belt tensioning and aligning capabilities.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 08/968,333, filedNov. 12, 1997, (pending), which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to planarization of semiconductor wafersusing a chemical mechanical planarization technique. More particularly,the present invention relates to an improved system and method forplanarizing semiconductor wafers consistently and efficiently over asingle integrated processing path.

Semiconductor wafers are typically fabricated with multiple copies of adesired integrated circuit design that will later be separated and madeinto individual chips. A common technique for forming the circuitry on asemiconductor wafer is photolithography. Part of the photolithographyprocess requires that a special camera focus on the wafer to project animage of the circuit on the wafer. The ability of the camera to focus onthe surface of the wafer is often adversely affected by inconsistenciesor unevenness in the wafer surface. This sensitivity is accentuated withthe current drive towards smaller, more highly integrated circuitdesigns. Wafers are also commonly constructed in layers, where a portionof a circuit is created on a first level and conductive vias are made toconnect up to the next level of the circuit. After each layer of thecircuit is etched on the wafer, an oxide layer is put down allowing thevias to pass through but covering the rest of the previous circuitlevel. Each layer of the circuit can create or add unevenness to thewafer that must be smoothed out before generating the next circuitlayer. Wafer fabrication is a delicate process that is sensitive tostray particulates and so is typically conducted in the highlycontrolled environment of a “clean room.”

Chemical mechanical planarization (CMP) techniques are used to planarizethe raw wafer and each layer of material added thereafter. Available CMPsystems, commonly called wafer polishers, often use a rotating waferholder that brings the wafer into contact with a polishing pad rotatingin the plane of the wafer surface to be planarized. A polishing fluid,such as a chemical polishing agent or slurry containing microabrasivesis applied to the polishing pad to polish the wafer. The wafer holderthen presses the wafer against the rotating polishing pad and is rotatedto polish and planarize the wafer.

While this primary wafer polishing process is important for waferfabrication, the primary wafer polishing alone is only part of the CMPprocess that must be completed before the wafer can be returned to aclean room. CMP process steps that must be completed before the wafercan be returned to the clean room will include cleaning and rinsing thepolishing fluid from the wafer followed by drying. Other steps beforethe final washing, rinsing and drying may include an additional polishutilizing different and non-compatible chemicals and slurries from theinitial polishing process as well as an additional polish process toremove fine scratches left by the previous polishing steps. Intermediaterinsing between these steps may be required as well. Existing devicesfor planarizing wafers are often discrete machines that take up largeamounts of space and require manual or semi-automated transport of thewafers from one machine to the next. Any delay in transferring wafersfrom one machine to another may allow the chemical slurry to begindrying thus creating great difficulties in polishing or scrubbing thewafers. Delays in wafer transfer between processes or machines can alsolet the chemical action of the chemical slurry last too long andadversely affect the polishing process.

Existing polishers and scrubbers have different wafer processing times.The polishing process usually takes a greater amount of time than thebuffing or scrubbing process. To optimize wafer process time andmaximize equipment utilization, some CMP processing schemes will utilizemultiple wafer polishers that each only complete a single planarizationstep. The wafers from these separate polishers are then each processedon the same buffer or scrubber. A problem with this technique is thatthe batches of wafers are processed on separate polish stations andinconsistencies in polish between the wafers are more likely. In orderto minimize these inconsistencies, existing CMP systems must haveextremely high tolerances for the equipment and must exactly reproducethe processing conditions at each polisher. The different wafer holdersmust be able to hold the wafers at the same angle and put the sameamount of pressure on the wafer when holding the wafer against thepolisher. The polishers must rotate at the same speed and provide thesame consistency and amount of polishing agent. Without carefultolerances, inconsistent CMP processing can occur with potentiallyharmful effects on the yield or performance of the semiconductorcircuits created from the wafer.

Accordingly, there is a need for a system and method of performing CMPon a plurality of semiconductor wafers in an efficient and consistentmanner.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, a method foruniformly planarizing and cleaning the surface of at least onesemiconductor wafer over a single process path is disclosed. The methodincludes the steps of providing a semiconductor wafer and asemiconductor wafer polishing system, mounting the semiconductor waferin the semiconductor wafer polishing system, and transporting thesemiconductor wafer to a wafer loading station. The wafer is transportedfrom the wafer loading station to a first primary polishing station anda first polishing procedure to partially planarize the semiconductorwafer is performed. The wafer is transported to a second polishingstation and a second polishing procedure completes planarization of thesemiconductor wafer. These steps are repeated for all wafers processed.In one alternative embodiment, each polishing station may utilize adifferent chemical polishing agent and process.

According to another aspect of the present invention, an apparatus forperforming chemical mechanical planarization of a plurality ofsemiconductor wafers implementing a single process path for each of theplurality of semiconductor wafers includes a first wafer transportmechanism for moving a semiconductor wafer from a load station to atransfer station. A second wafer transport mechanism is positionedadjacent the transfer station and is designed to move the semiconductorwafer from the transfer station to a semiconductor wafer loading device.The wafer loading device loads individual wafers onto a wafer conveyor.The wafer conveyor has a number of wafer receiving areas and isrotatably movable to receive a semiconductor wafer in each of theplurality of wafer receiving areas. The wafer conveyor is arranged in amanner to allow continuous closed loop motion of the wafers along apredetermined process path and is optimized to avoid any need tobacktrack along the process path. A first primary polishing stationpositioned along the process path planarizes a semiconductor wafer overa predetermined time to produce a partly planarized semiconductor wafer.A second primary polishing station positioned along the process pathcompletes the planarization of the partly planarized semiconductor. Atouch-up polisher buffs the planarized wafer to remove any tracescratches left by the first and second primary polishing stations.Preferably, the wafers are also rinsed in a wafer conveyor loader andscrubbed and dried in a wafer scrubbing device to completely removeslurry and particulates. Each of the semiconductor wafers travels thesingle process path.

In a preferred embodiment, a semiconductor wafer transfer mechanism fortransporting a semiconductor wafer between a wafer conveyor and a waferprocessing point is disclosed. The transfer mechanism includes arotatable, axially movable spindle. A lever arm is attached to thespindle having one end connected to a movable frame and a second endconnected to a fine adjustment spindle driver attached to the movableframe. A coarse adjustment spindle driver is attached to a fixed frameand connected to the movable frame so that the coarse adjustment spindledriver can move the movable frame relative to the fixed frame in anaxial direction of the spindle. The semiconductor wafer transfermechanism preferably cooperates with detachable wafer carrying heads anda rotatable wafer conveyor to move wafers between the wafer conveyor anda polishing station or wafer conveyor loader. The coarse and fineadjustment spindle drivers provide an added degree of control over thepressure on a wafer held against a polishing pad at a polishing station.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a semiconductor polishing systemaccording to a preferred embodiment of the present invention.

FIG. 2 is a left side elevational view of the wafer polishing system ofFIG. 1.

FIG. 3 is a schematic illustrating a preferred wafer processing flowpath in the wafer polishing system of FIGS. 1 and 2.

FIG. 4 is a perspective view of a preferred index table for use in thesystem of FIGS. 1 and 2.

FIG. 5 is a perspective view of a second preferred embodiment of anindex table for use in the system of FIGS. 1 and 2.

FIG. 6 is a bottom perspective view of a wafer head assembly.

FIG. 7 is a top perspective view of the wafer head assembly of FIG. 6.

FIG. 8 is a top view of a head retainer assembly and head assembly usedin the wafer polishing system of FIG. 1.

FIG. 9 is a cross-sectional view of the head retainer assembly and headadapter of FIG. 6 taken along line 9—9 of FIG. 8.

FIG. 10 is a partial top view of head retainer operating pistonspositioned adjacent a head retainer mechanism on the index table of FIG.4.

FIG. 11 is a top plan view of a second preferred head retainer mechanismfor use with the system of FIG. 1.

FIG. 12 is a top plan view of a second preferred tool adapter connectorfor use with the head retainer mechanism of FIG. 11.

FIG. 13 is a cross sectional view of a head assembly mounted in the headretaining mechanism of FIG. 11.

FIG. 14 is a side elevational view of a preferred head loader assemblyfor use in the wafer polishing system of FIG. 1.

FIG. 15 is a rear perspective view of a preferred spindle drive assemblyfor use in the wafer polishing system of FIG. 1.

FIG. 16 is a side elevational view of the spindle drive assembly of FIG.15.

FIG. 17 is a cross-sectional view of the spindle drive assembly takenalong line 17—17 of FIG. 16.

FIG. 18 is a schematic view of a preferred spindle drive assemblyelectrical and pneumatic control circuit.

FIG. 19 is a side elevational view of a preferred head loader spindledrive assembly for use in the system of FIG. 1.

FIG. 20 is a top perspective view of a preferred primary wafer polishingdevice for use in the wafer polishing system of FIGS. 1 and 2.

FIG. 21 is a cross-sectional view taken along line 21—21 of FIG. 20.

FIG. 22 is a partial perspective view of the primary wafer polishingdevice of FIG. 20.

FIG. 23 is a cross-sectional view taken along line 23—23 of FIG. 20.

FIG. 24 is a schematic view of a preferred electrical and pneumaticcontrol circuit for the primary polishing device of FIG. 20.

FIG. 25 is a perspective view of a preferred deflection roller for usein the primary polishing device of FIG. 20.

FIG. 26 is a perspective view of a preferred platen assembly for use inthe primary polishing device of FIG. 20.

FIG. 27 is an exploded view of the platen assembly of FIG. 26.

FIG. 28 is a perspective view of a preferred platen adjustment lifterused in the primary polishing device of FIG. 20.

FIG. 29 is a top plan view of a preferred touch-up polisher for use inthe wafer polishing system of FIG. 1.

FIG. 30 is a front view of the touch-up polisher of FIG. 29.

FIG. 31 is a block diagram of the control circuitry and communicationpaths used in the wafer polishing system of FIGS. 1 and 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of a wafer polishing system 10 is illustrated inFIGS. 1-3. The system 10 has a front end frame assembly 12 and a backend frame assembly 14 connected to the front end frame assembly 12. Thesystem 10, typically used in a semiconductor wafer fabrication facility,receives semiconductor wafers from at least one wafer holder, such as acassette 16 or a cassette holder such as an Ergo loader available fromHine Design, Inc., positioned on the end of the front end frame assembly12. As will be explained in greater detail below, the semiconductorwafers are retrieved from the cassettes 16 completely processed, andreturned to the cassettes 16, to the same or predetermined differentlocation, in a clean, dry, and uniformly planarized condition by thesystem 10.

The front end frame assembly 12 is sized to accept the desired sizewafer cassette 16. Each cassette 16 contains multiple wafers. Thecassettes 16 may be loaded manually at an input/output queue, orautomatically using a standard module interface (SMIF) carrier 18. Anynumber of cassettes 16 may be used with the preferred wafer polishingsystem and the cassettes can be constructed from a plastic such aspolypropylene, a Teflon material, or any other material suitable to holdthe wafers. A dry environment robot 20 is positioned inside the frontend assembly 12 adjacent to the cassettes 16. The dry robot 20 ispreferably designed to retrieve wafers from and return wafers to thecassette 16. One suitable robot 20 for use in the front end assembly 12is a model no. 04300-038 manufactured by Hine Design, Inc. A wafertransfer station 22 positioned inside the front end assembly 12 betweenthe dry robot 20 and the back end assembly 14 receives wafers from thedry robot during processing. The transfer station 22 preferably includesa wafer receiving platform suitable for receiving a semiconductor waferfrom the dry robot 20. The transfer station 22 pre-aligns the wafer andis configured to permit access to a wet environment robot 24 located inthe back end assembly 14. Suitable transfer stations are available fromHine Design, Inc.

The front end assembly 12 also contains a display 26 showing the graphicuser interface (GUI) 28 for operating the entire wafer polishing system10. The GUI is preferably located adjacent to the cassettes 16 on theportion of the front end assembly projecting into the clean room. TheGUI 28 preferably allows users to interact with the system 10 to varyprocessing parameters and monitor progress. The display 26 may be astandard cathode ray tube, liquid crystal display or other suitablevisual display device.

A filter 30, preferably a high efficiency particulate attenuator (HEPA)filter is mounted in the front end assembly 12 to prevent particulatesfrom contaminating the wafer. Also, a scrubber assembly 32 is positionedin the front end assembly 12 with one end adjacent to the back endassembly 14 and the other end adjacent to the dry robot 20. The scrubbermechanically and chemically cleanses wafers that have been processed inthe back end assembly and then rinses and dries the wafers before thedry robot returns them to the cassettes 16. Wafers emerging from theback end assembly often require mechanical scrubbing to thoroughlyremove the particles of chemical slurry left over from the polishing orbuffing process occurring in the back end assembly 14. One suitablescrubber is the double side scrubber (DSS®) manufactured by OnTrakSystems, Inc. An advantage of the presently preferred method and systemis the “dry in—dry out” processing of wafers where wafers are placedinto and removed from the system in a dry, particulate free condition.

As described above, the semiconductor wafers are transferred from thefront end assembly 12 to the back end assembly 14 via a wet robot 24.The term “wet” refers to the wet environment the robot operates in. Thiswet environment is created by the presence of chemicals, moisture andhumidity used and generated during the polishing and buffing of wafersin the back end assembly 14. Although a single robot could be used tohandle wafer transfer between the cassettes 16 and the processingstations in the system 10, two robots 20, 24 are preferred to improveisolation of chemical slurry and particulates from the cassettes and anyprocessed wafers. One suitable wet robot 24 is a model no. 04300-25manufactured by Hine Design, Inc.

In the back end assembly 14, the wet robot 24 cooperates with a headloader 34 as best shown in FIG. 3. The head loader 34 is capable ofloading and unloading semiconductor wafers onto a wafer conveyor device,preferably a rotatable index table 36 as shown in FIG. 4. The indextable 36 releasably holds multiple wafers, each wafer being heldseparately from the others. The index table 36 travels in one directionto carry each wafer through the complete circuit of processing stationsbefore returning to the head loader 34 where the fully polishedsemiconductor wafer is unloaded and transferred back to the cassettes 16through the front end assembly 12. The first and second processingstations along the path of the index table 36 in the back end assembly14 are primary wafer polishing devices 38, preferably linear waferpolishers capable of chemical mechanical planarization (CMP). Althoughlinear polishers are preferred, other types of polishing devices, suchas rotary polishers, may be readily implemented in the modular design ofthe wafer polishing system 10. For purposes of this disclosure, primarywafer polishing devices refer to polishers configured to remove materialfrom a wafer at a rate of at least 1,000 angstroms per minute (Å/min.)

After the index table transports a wafer to each of the primary waferpolishing devices, the index table 36 transports the wafer to the thirdprocessing station, preferably a touch-up polishing device 40 such as arotary buffer. A suitable touch-up polishing device 40 is an orbitalpolisher available from Guard, Inc. Any of a number of rotary or lineartouch-up polishing devices may be utilized. For purposes of thisdisclosure, the term touch-up polishing device refers to a wafer buffingdevice that removes residual scratches left on the surface of the waferfrom the primary polishing steps at a rate less than 1,000 Å/min., andmost preferably at a rate between 50-500 Å/min. The above generaldescription of the components in the back end assembly 14 will be setforth in greater detail below. The term processing station as used belowis intended to generally refer to any of the head loader 34, primarypolishing devices 48, and touch-up polishing device 40.

Wafer Conveyor

FIG. 4 best shows a first preferred embodiment of an index table 36 thatis mounted in the back end frame assembly 14 over all of the primary andtouch-up polishing devices 38, 40. As mentioned above, the index table36 operates to convey semiconductor wafers to each processing station sothat all semiconductor wafers go through the same processing steps onthe same processing stations. The index table 36 preferably has aplurality of head receiving areas 42 equally spaced around the indextable. The index table 36 has a central hub 44 that connects to arotating shaft 46 (FIG. 2) via a motor driven indexer 45 mounted aboveor below the index table 36. The index table 36 is preferably mountedbelow the motor driven indexer 45. This configuration of index table 36and indexer 45 permits a more compact grouping of processing stationsbelow the index table. This configuration also prevents potentialcontaminants from dripping down from the index table into the indexer orbearing assembly. The index table 36 is rotatable in precise incrementsin one direction through continuous 360° rotations by a motor connectedto the motor driven indexer 45. The motor 47 connected to the indexer 45drives the indexer through 90° rotations in the embodiment shown. Inother embodiments, smaller or larger rotational increments may beexecuted using an appropriately selected indexer. For example, if morethan four wafer receiving areas, and thus more than four wafers, arepositioned on the index table 36, the rotational increment may beproportionately designed to ensure precise placement of each wafer overa processing station positioned below the index table. The index table36 most preferably travels in one direction and does not reversedirection during the wafer polishing process.

A rotary feedback system 49 monitors the position of the index table 36.The rotary feedback system consists of a rotary encoder 51 connected tothe rotating shaft 46 by an encoder drive sprocket in 53 and encoderdrive chain 55. Signals from the rotary encoder 51 are routed to atransport module controller 316 (See FIG. 31) that monitors the progressof the wafers and controls the motor 47 driving the indexer 45. Plasticcoated aluminum or stainless steel are suitable materials for the indextable. A motor driven indexer, such as the Camco 902RDM4H32-330, may beused to accurately rotate the index table.

In another preferred embodiment, the wafer conveyor may be an indextable 436 configured to have a lighter weight as shown in FIG. 5. Inthis embodiment, the index table 436 uses a frame made up of supportarms 448 extending from the central hub 444 rather than a solidmaterial. The wafer receiving areas 442 are positioned on the ends ofthe support arms 448. Circumferentially placed supports 450 add strengthand rigidity to the index table 436. As will be evident to those ofordinary skill in the art, other index table configurations may beimplemented.

Head Assembly and Head Retaining Assembly

The semiconductor wafers, when proceeding along the process path definedby the index plate, are each held by a different head assembly 52. Eachhead assembly 52, as shown in FIGS. 6 and 7, holds one wafer. FIG. 6shows the wafer receiving plate 54 of the head assembly 52. When holdinga wafer, the head assembly 52 retains the wafer against the waferreceiving plate 54 within the boundary defined by the retaining ring 56that surrounds, and extends beyond, the plane of the wafer receivingplate 54. A plurality of perforations, or fluid conduits 58, aredistributed around the wafer receiving plate 54. These fluid conduits 58assist the head assembly 52 in retaining the wafer either throughsurface tension or a partial vacuum created between the wafer andreceiving plate 54. An outer ring 60 and head adapter 66 hold the lowerportion of the head assembly 52 together. As shown in FIG. 7, slots 64and concentric protruding rings 62 are positioned on the head adapter66.

The slots 64 and rings 62 permit the head adapter 66 to removablyconnect to a tool changer adapter 80. The interconnection of the headassembly adapter and tool changer adapter is best shown in FIGS. 8 and9. The head adapter 66 is designed to connect the head. The tool changeradapter 80 is preferably designed to mate with the head adapter 66 onone side and the female half of a standard two-piece tool changer on theother side. One suitable two-piece tool changer is available fromRobotic Accessories of Tipp City, Ohio. An advantage of the present headassembly 52 is that any of a number of commonly available wafer holdingheads and tool changers may be used by fashioning an appropriate headadapter plate or tool changer adapter 80.

Referring to FIGS. 4, 8 and 9, the tool changer adapter 80 alsoreleasably connects to the head retainer assembly 68 attached to eachhead receiving area 42 on the index table 36 and thus connects the headassembly 52 to the index table 36. The head retainer assembly 68consists of an annular wall 70 mounted with screws 72 to the index table36. Although FIG. 4 only shows one head retainer for illustrationpurposes, a head retainer assembly 68 is preferably mounted at eachwafer receiving area 42 on the index table 36. In one preferredembodiment, a slotted ring 74 is fixedly positioned in the annular wall70, where the ring 74 is made from a metal material and the wall 70 ismade from a plastic material to reduce weight. The annular wall 70 isconnected to two projections 76 that extend from the annular wall 70.The projections 76 are movable to rotate the wall 70 and attached ring74. The rotation retracts ball bearings 78 holding the tool changeradapter portion 80 of the head assembly. Slots in the slotted ring 74receive the ball bearings 78 and allow the spindle drive assembly 108(FIG. 16) to engage and move the head assembly down to the processingstation. When the wafer is received at the index table from theprocessing station, the head assembly 52 is reconnected to the headretaining mechanism 68. This is accomplished by again pushing on theprojections 76 to rotate the annular wall 70 and slotted ring 74 andbring the ball bearings in contact with the annular groove 79 around thetool changer adapter portion 80 of the head assembly 52.

The head retainer assembly 68 also provides for a DI water rinse of thewafer and head assembly during rotation of the wafer on the index table.A DI water port 69 on the outside of the head retainer assembly receivesDI water from tubing (not shown) on the index table 36. Referring toFIG. 9, the DI port 69 connects with a circumferential channel 71 toprovide DI water to the head assembly. A passage 73 in the headretaining assembly opens up on a rinse gap 75 between the head assembly52 and the head retainer assembly 68. DI water, or other desiredcleaning agent, can be fed into the DI port 69 and flows out on thewafer and head assembly 52 to remove leftover cleaning agents. Thecleaning process can occur while the wafers are traveling betweenprocessing stations and thus facilitates the use of chemicallyincompatible polishing agents at different processing stations.

As shown in FIG. 10, a pair of head retainer operating pistons 59cooperate with the projections 76 on the head retainer assembly 68 tolock or unlock the head assembly to the head retainer assembly. A pairof head retainer operating pistons 59 are located on the frame of theback end assembly adjacent to each processing station in the system 10.The pistons are fastened by brackets 61 to the frame and do not travelon the index table. The pistons are mounted to align with each headretainer mechanism when the incremental rotational movement of the indextable brings each of the wafers currently mounted in the index table tothe next respective processing station. The pistons 59 each have acontact head 63 on the end of a shaft 65 designed to push against aprojection 76 and thereby lock or unlock the head assembly from theindex table 36. Any of a number of commonly available pneumatic orhydraulic pistons may be used. The pistons 59 are preferably controlledby the transport module controller 316 (FIG. 31) to lock or unlock thehead assembly 52 in coordination with the spindle drive assembly 108,109 (see FIGS. 15-19).

FIGS. 11-13 illustrate a second preferred embodiment of a head retainerassembly 468. In this embodiment, separate head retainer operatingpistons are unnecessary. As shown in FIG. 11, the head retainer assembly468 includes a head assembly connecting ring 469 that attaches to theannular wall 470 at each head receiving area of the index table. Thering 469 has an inner flange 471 with a plurality of tool changeradapter pass through slots 472 disposed in an asymmetric pattern aboutthe inner flange 471. The pass through slots 472 are designed to receivepins 474 extending radially from the outer circumference of a toolchanger adapter 480 attached to the head assembly. Each pass throughslot 472 is spaced a predetermined circumferential distance from a pinretaining bay 473. Each pin retaining bay is defined by an indentedportion on the inner flange 471.

As explained in greater detail below, the spindle drive assembly at eachprocessing station locks the head assembly in the head retainermechanism of FIGS. 11-13 by aligning the pins 474 on the tool changeradapter with the pass through slots 472, lifting the head assembly untilthe pins 474 pass through the pass through slots 472, and rotating andthen lowering the head assembly until the pins come to rest in the pinretaining bays 473. The asymmetric pattern of slots and correspondingpins provides for a polarized fit to insure each head assembly is loadedonto the index table in the same orientation for every transfer of thehead assembly between the index table and a processing station. The headretainer assembly shown in FIGS. 11-13 is advantageous in that noseparate pistons are required to lock or unlock the head retainerassembly. Instead, the spindle drive assemblies perform the necessarysteps of aligning and locking the head assembly on the index table.

Head Loader

FIG. 14 illustrates the head loader 34 interacting with the headassembly 52 and index table 36 during a load/unload maneuver. Forsimplicity, FIG. 14 does not show the entire head assembly 52 or thehead loader spindle drive assembly 109 (FIG. 19) connected to the headassembly 52. The head loader 34 is designed to put a pre-aligned waferonto the head assembly prior to polishing and to remove a wafer after ithas been polished and buffed. Additionally, the head loader functions asa rinsing station to rinse excess slurry off of the head assembly andwafer with deionized (“DI”) water when unloading the wafer. Othercleansing chemicals, separately or in combination with DI water, may beapplied by nozzles in the head loader 34. The head loader 34 consists ofa vertically moveable rinse containment tub 90 surrounding a wafertransfer assembly 92. The transfer assembly 92 includes a cylindricalsupport ring 94 coaxially aligned with an alignment ring 96. A cylindershaft 102 driven by a pneumatic cylinder 98 mounted on the frame 99connects to the tub 90. The cylinder 98 lifts and lowers the tub.Preferably, the cylinder 98 can lift the tub 90 up to the bottom of theindex plate 36 to form a seal with the index plate. The seal isnecessary to allow the wafer and head assembly to be flushed during anexchange between the head loader and index plate. The seal may be anO-ring 91 positioned around the opening of the tub 90.

Inside the tub, the head alignment and wafer support rings 96, 94 aremovable independently of the tub by a linear actuator 97 via a lifterrod 101. The linear actuator 97 moves both the alignment ring 96 andwafer support ring 94. The linear actuator 97 raises the head alignmentring 96 and wafer support ring 94 until the head alignment ring 96engages and aligns the wafer support ring 94 with the head assembly 52.Once alignment is achieved with the head assembly 52, a second actuator121 independently raises the wafer support ring 94 to transfer the waferto, or accept the wafer from, the head assembly The wafer and headassembly receive a rinse from spray nozzles 100 positioned on a support103 adjacent the head alignment and wafer support rings 96, 94.Preferably, the nozzles spray DI water, and additional cleaningchemicals such as a surfactant, to rinse the polished wafer clean andalso rinse the head before transferring an unpolished wafer forprocessing onto the head.

Sindle Drive Assemblies

In addition to the head loader raising or lowering a wafer to the indextable 36, a spindle drive assembly lowers the head assembly 52 from theindex table. Two types of spindle drive assemblies are preferably usedin the presently preferred system 10. A first type of spindle driveassembly is positioned opposite the head loader 34. A second type ofspindle drive assembly is positioned at each of the remaining processingstations along the process path defined by the index table. Both typesof spindle drive assemblies detachably connect a spindle to the headassembly from above the index table using a robotic tool changer havinga male portion 81 connected to the spindle 110 and a female portion 83attached to each head assembly 52.

FIGS. 1 and 2 best show the location of the spindle drive assemblies 108for the primary polisher and touch-up polisher used in the waferpolishing system 10. Although the spindle drive assembly at the headloader 34 is preferably a simplified version of the spindle driveassembly 108 at the other processing stations, the more complex spindledrive assembly 108 may also be used at the head loader. As describedabove, the head assembly 52 is removably attachable to the rotatableindex table by a head retainer assembly 68. At each processing stationalong the path of the index table, a spindle drive assembly 108 engagesthe head assembly, holds the head assembly 52 while it is unlocked fromthe head retainer assembly on the index table 36, and moves the unlockedhead assembly 52 and wafer down to the processing station. After theprocessing at the processing station is complete, the spindle driveassembly 108 lifts the head assembly and wafer back up to the indextable, locks the wafer and head assembly into the head retainermechanism, and disengages from the head assembly. The index table maythen freely rotate to the next index point and the process ofdisengaging the wafer and head assembly from the index table repeatssimultaneously at each processing station in the wafer polishing system10.

Alternatively, the spindle drive assembly 108 can unlock or lock thehead assembly directly if the head retainer mechanism of FIGS. 11-13 isused. The spindle drive assembly 108 rotates the head assembly until thepins 474 align with the pass through slots 472. The spindle driveassembly can then raise the head assembly slightly and rotate it untilthe pins rest in the pin retaining bays 473 on the flange 471. Thespindle drive assembly may then release the head assembly bydisconnecting from the female portion of the tool changer. The processis reversed when the head assembly is again grabbed by the spindle driveassembly at the next processing station and lowered for processing. Anadvantage of the presently preferred system 10 is that the wafers beingprocessed can be simultaneously moved between processing stations usingthe detachable head assemblies, without the need to try and move theweight and bulk of the entire spindle drive assembly.

A preferred spindle drive assembly 108 is shown in detail in FIGS.15-18. The spindle drive assembly 108 includes a spindle 110 extendingvertically through the assembly 108. The spindle 110 is rotatably andslidably mounted in a pair of bearing assemblies 112 positioned towardsopposite ends of the spindle 110. The bearing assemblies are preferablyball spline bearings that allow the spindle 110 to slide along, androtate about, its axis. One suitable ball spline bearing is the type LTRbearing available from THK, Inc.

As shown in FIG. 17, the spindle 110 has a hollow bore 114 extending thelength of the spindle 110. A plurality of fluid conduits 116 arepositioned in the hollow bore 114. The fluid conduits 116 may hold airor a liquid, or may hold a vacuum. Depending on the type of headassembly 52 used with the system 10, some or all of these conduits 1 16will be utilized. A rotator coupling 118 is attached to the end of thespindle 110 opposite the head assembly 52. Flexible tubing (not shown),carrying any fluid or vacuum desired, attaches to the rotator coupling118 and connects to the conduits 116 on the spindle 110.

The spindle 110 is rotated by a servo gear motor 120 fixed to the frameof the spindle drive assembly 108. The servo gear motor 120 turns a belt(not shown) that, in turn, rotates an adapter drive pulley 122 connectedto the spindle 110. Axial movement of the spindle 110 is controlled by acoarse adjustment mechanism 124 and a fine adjustment mechanism 126. Thecoarse adjustment mechanism 124 is preferably a screw drive actuatorsuch as a BC35 screw-drive actuator available from Axidyne. The coarseadjustment mechanism moves the spindle 110, fine adjustment mechanism126, bearing assemblies 112 and the rest of the spindle drive assembly108 on rails 130 attached to a fixed frame 132. The coarse adjustmentmechanism 124 is attached to the fixed frame 132 and has a drive portionattached to slide bearings slidably connecting the remainder of thespindle drive assembly 108 to the rails 130. In a preferred embodiment,the coarse adjustment mechanism 124 is designed to move the spindle,along with the remainder of the spindle drive assembly 108,approximately 3-4 inches so that the head assembly 52 is brought downthrough the index table adjacent the primary wafer polishing device 38or touch-up polishing device 40.

Once the head assembly 52, via the coarse adjustment mechanism 124,reaches approximately down to the processing area, the fine adjustmentmechanism 126 moves the wafer the remainder of the distance and controlsthe downforce applied on the wafer. Preferably, the fine adjustmentmechanism 126 is actuated by a diaphragm double acting cylinder 134attached to a lever arm 136. The lever arm is attached to the cylindershaft 138 at one end and a pivot point 140 fixed on the rails 130 at theother end. A throw-out bearing 142 is connected to the lever arm 136between the pivot point 140 and cylinder shaft 138. The throw-outbearing 142 has an axially fixed, rotatable connection to the spindle110 so that the cylinder 134 can move the spindle 110 up or down whilethe spindle 110 rotates. The lever arm provides advantages of permittinga smaller, lighter, less powerful, cylinder, or other type actuator, tobe used while also increasing the axial resolution, or fine adjustmentability, of the cylinder. In one preferred alternative, a highresolution, fast acting lead screw can replace the double actingcylinder 134 on the fine adjustment mechanism 126. One suitablediaphragm double acting cylinder is the model D-12-E-BP-UM double actingcylinder available from Bellofram.

Because of the importance of maintaining a controlled downforce on thewafer at each wafer polishing device 38, the fine adjustment mechanismpreferably is controllable to within one-half pound per square inch(p.s.i.) and has a range of 2 to 10 p.s.i. An alternatively preferreddevice for use as a fine adjustment mechanism is a high resolutionlinear actuator. A linear displacement sensor 141 mounted on the fixedframe 132 provides electrical feedback to a control circuit indicatingthe movement and position of the coarse adjustment mechanism 124. Acylinder extension sensor 143 is located on the fine adjustmentmechanism 126 and provides an electrical signal to a control circuitindicating the position of the lever arm 136 to the cylinder 134.Preferably, the electrical signal indicating the position of the leverarm and cylinder is utilized to maintain the cylinder shaft 138 in thecenter of its range of motion. Additionally, the spindle rotates thewafer at approximately 5 to 50 r.p.m. during the primary polishing andbuffing (touch-up polishing) procedures while the spindle drive assemblymaintains the desired downforce.

In order to maintain proper control of the spindle and downforce appliedto a wafer on the spindle drive assembly 108, a closed loop controlcircuit 144 is used as shown in FIG. 18. The control circuit 144includes a coarse motion control circuit 146, a spindle rotation controlcircuit 148, and a head downforce control circuit 150. The coarse motioncontrol circuit 146 is electrically connected to the motor of the coarseadjustment mechanism 124 to control speed and duration of motion. Alower limit sensor 152 and an upper limit sensor 154 communicate withthe coarse motion control circuit 146 to cut off the coarse adjustmentmechanism 124 when extreme positions are reached. The lineardisplacement sensor 141 and cylinder extension sensor 143 communicatewith the control circuit. A plurality of control lines 156 alsocommunicate instructions from a process module controller 314 (FIG. 31)in communication with the GUI 28 on the system 10. The spindle rotationcontrol circuit 148 controls the motor 120 connected to the spindle 110via a belt and adapter. A plurality of motor control lines 158 enableand instruct the motor 120 to rotate the spindle in the desireddirection at the desired speed.

The fine adjustment mechanism 126 is controlled by a head downforcecontrol circuit 150. To best control the pressure, in a preferredembodiment, the control circuit 150 monitors a pressure differential oneither side of the diaphragm in the double acting cylinder 134 on apressure transducer 160 and activates a control valve 162 to add orremove pressure from either side of the diaphragm. Preferably, thecylinder is a pneumatic cylinder although a hydraulic cylinder may alsobe used. A separate head downforce sensor, such as a load cell, may alsobe used to measure absolute pressure applied by the fine adjustmentmechanism 126. The pneumatic pressure supplied to the control valve 162is delivered through a pressurized line 164 that is activated through asolenoid switch 166 after the coarse adjustment mechanism completes itstravel. A control line 168 instructs the head downforce circuit 150 toraise or lower the spindle 110 and how much force to apply based oninstructions received from the user through the GUI 28.

In a preferred embodiment, a head loader spindle drive assembly 109 ispositioned over the head loader 34. The head loader spindle driveassembly 109, as shown in FIG. 19, is a simplified version of thespindle drive assembly of FIGS. 15-17. The head loader spindle driveassembly 109 includes a spindle 111 rotationally mounted in a bearingblock 113. The bearing block 113 is slidably mounted on a verticallyoriented rail 115 affixed to the support strut 117. The support strut117 attaches via fasteners to the frame of the wafer polishing system10.

The head loader spindle drive assembly 109 uses a single linear actuator119 to move the spindle 111, bearing block 113, and attachments to thebearing block perpendicular to the plane of the index table. Unlike thespindle drive assembly 108 of FIGS. 15-17, no fine adjustment mechanismis necessary because no polishing is performed at the head loader.Additionally, the head loader spindle drive assembly 109 only rotatesthe head assembly +/−360°. Because continuous revolutions in onedirection are not necessary at the headloader, the head loader spindledrive assembly 109 does not use a rotator coupling to guide a fluid orvacuum down the spindle 111. Instead, any fluid or vacuum conduits aresimply routed externally of the spindle 111 and provided with enoughslack to allow up to a +/−360° turn of the spindle. A servo motor 127drives a belt and pulley system 123 via a gear box 125 to turn thespindle 111. As described above, the spindle 111 rotates to allow thenozzles in the head loader to rinse the wafer and/or head assembly. Thepresently preferred head loader spindle drive assembly 109 offers theadvantages of reduced cost and complexity in comparison to the spindledrive assemblies 108 necessary at the primary and touch-up polishers 38,40.

Primary Wafer Polishing Device

The spindle drive assemblies 108 cooperate with the processing stationspositioned at each point along the process path defined by the indextable. As shown in FIGS. 1-3, two of the processing stations are primarywafer polishing devices 38. Preferably, the primary wafer polishingdevices 38 are linear polishers designed for CMP processing ofsemiconductor wafers. The wafer polishing system 10 may incorporaterotary polishers in an alternative embodiment. A preferred linear waferpolishing device 38 is shown in FIGS. 20-25. The primary wafer polisher38 includes a belt 178 positioned around a drive roller 180 and an idleroller 182. The belt is preferably constructed from a high tensilestrength material, for example a polymer or stainless steel material.The belt 178 is approximately 13-14 inches wide when polishing a waferof twelve inches or less in diameter. An absorbent pad 179 covers thebelt 178 and cooperates with a polishing fluid such as a chemical agentor slurry containing micro abrasives to remove material from the surfaceof a wafer. Preferably, each primary wafer polisher 38 used in the waferpolishing system is configured to remove material from the surface of awafer at a rate of at least 1,000 angstroms per minute (Å/min.)Additionally, each polisher 38 preferably incorporates a pad conditioner(not shown) to roughen the pad 179 surface, provide micro-channels forslurry transport and remove debris generated during the CMP process. Anyof a number of known pad conditioners may be used.

The rollers 180,182 are mounted in a lined steel frame 184. The frame184 is preferably made out of stainless steel plates and has a lining186 made of a plastic or plastic coated material. Because chemicalslurry, an abrasive substance, is used with the wafer polisher 38, thepolisher is sealed as much as possible both inside and outside so as toprevent the abrasives and particulates generated during polishing fromgetting into delicate bearing assemblies or contaminating the back endassembly 14. A protective guard 188 covers the ends of the rollers180,182. Both rollers 180,182 have a tubular core 190 made of stainlesssteel or other non-corrosive, high strength material. A rubber coating192 is formed over the tubular core 190 to provide traction between thebelt 178 and rollers 180,182. Preferably, the belt 178 overhangs theends of the rollers 180,182 to prevent water and chemical slurry fromseeping between the belt 178 and rollers 180,182. Additionally, therubber coating may have a grooved surface to prevent a hydroplaningeffect if water or slurry does get between the belt and rollers. A drain194 for excess water and slurry is located at the bottom of the frame184.

A roller drive gear motor 196 is positioned below the drive roller 180outside of the frame 184. The motor 196 turns a drive belt 198connecting the motor to the drive axle 200 of the roller 180. The driveaxle is rotatably mounted on sealed bearing assemblies 202 in the frame184. The tubular core 190 of the roller 180 is rigidly attached to thedrive axle 200.

Unlike the drive roller 180, the idle roller 182 has an axle 204 thatdoes not rotate. The tubular core 190 of the idle roller 182 passivelyrotates about the axle 204 on sealed bearings 206 positioned between thetubular core 190 and axle 204. The tension of the belt 178 on the idleroller 182 turns the idle roller synchronously with the drive roller180. Each end of the axle 204 on the idle roller 182 is pivotallyattached to slide bars 206 slidably mounted on the frame 184 as shown inFIG. 22. The slide bars 206 are part of a steering and tensioningmechanism 208 in the polisher 38 described below.

As best shown in FIGS. 21-22, the tension and alignment of the belt 178on the rollers 180,182 is automatically adjustable with the steering andtensioning mechanism 208. The steering and tensioning mechanism 208 ismade up of a pneumatic cylinder 210, such as a multi-stage air cylinderavailable from STARCYL, connected to each slide bar 206 via a linkageassembly 212. The linkage assembly 212 preferably houses a load cell 214to monitor load at each side of the idle roller 182. The slide bars 206are each held in a take-up housing 216 mounted on each side of the frame184 adjacent the ends of the idle roller axle 204. The take-up housingconsists of two sealed linear bearing assemblies 218 mounted on oppositesides of the opening in the housing for the axle 204. The bearingassemblies are preferably aligned to allow movement of the slide bars206 in a linear direction parallel to the plane of the rollers 180,182.

As shown in FIG. 21, the slide bars and idle roller axle cooperate topermit the ends of the idle roller axle to move independently of eachother. To adjust overall tension on the belt 178, the pistons 210 canmove the slide bars 206 away from or towards the drive roller 180. Thisadjustment may be done automatically without the need for any handadjustments or dismantling of the rollers. Concurrently with the tensionadjustment, the steering and tensioning mechanism 208 can steer the idleroller with respect to the drive roller so that the belt maintains itsproper alignment on the rollers and does not travel off one end. Thesteering is accomplished through independently moving the slide barswith the pistons 210 to align the belt 178 as it rotates about therollers. The steering adjustments are made in accordance with signalsreceived from alignment sensors 244 (FIG. 24) placed over one or bothedges of the belt 178. Any of a number of sensors may be used tocomplete a closed loop circuit that controls the relative movement andsteering of the idle roller.

As best shown in FIGS. 21-22, the slot 219 on either end of the idleroller axle 204 receives the slide bar 206 and is connected to the slidebar at a rotatable junction, preferably a pin 220 passing through theslide bar 206 and axle 204. A gap 222 between the base of the slot 219in the axle 204 and the edge of the slide bar 206 provides clearance forpivoting movement of the idle roller axle 204 about each pin 220 whenthe steering and tensioning mechanism 208 requires the ends of the idleroller 182 to move independently of each other. A flexible annular seal224 seals the gap between the axle 204 and the opening in the frame 184for the axle. The flexible seal 224 also provides for the linearmovement of the axle during steering and tensioning adjustments. As anadditional source of information regarding tensioning and steering ofthe belt 178, the belt tensioning and steering mechanism 208 includes alinear displacement sensor 226 on each end of the idle roller axle 204.A fixed portion 228 of the sensor 226 preferably attaches to the take-uphousing 216 and a movable portion 230 is attached to the slide bar 206.

Electrical signals indicative of each slide bar's 206 position relativeto a known starting point are sent by each sensor to a steering andtensioning control circuit 232 as shown in FIG. 24. The steering andtensioning control circuit 232 on each polisher 38 manages thedistribution of pressurized air in a pressurized air line 234. Asolenoid valve 236 is remotely triggered by a data signal when thepolisher is activated. A pressure switch 238 monitors the air pressureto make sure that a predetermined sufficient air pressure is present.Data signals from the load cells 214 on the linkage assemblies 212 areused by the central processor (not shown) to adjust pressure controlvalve 240. The pressure control valve 240 varies the tension placed onthe belt by the pneumatic cylinders 210. Concurrently, a belt trackingcontroller 242 receives information from the belt edge position sensor244, preferably an inductive proximity sensor, via an amplifier circuit246. In one preferred embodiment, the belt edge position sensor may bean optical sensor, such as a video camera, positioned to monitor thebelt edge position and provide an electrical signal related to thebelt's position to the belt tracking controller.

The belt tracking controller 242 electrically controls a belt trackingcontrol valve 248. The control valve 248 will distribute the airpressure to each cylinder 210 in accordance with the steering needsindicated by the belt tracking controller. Preferably, the feed backloop from the belt edge position sensor 244 to the belt trackingcontroller 242 provides an adjustment signal to the belt trackingcontroller in the range of 4-20 mA with a quiescent, or belt center,level set at the midpoint of this range. Pressure gauges 250 on thepneumatic lines between the cylinders 210 and control valve 248 permitmanual inspection of the present pressure settings.

In addition to the tension and steering concerns, the belt 178 needs tobe kept as flat as possible when the wafer is lowered down from theindex table by the spindle drive assembly 108. As mentioned previously,the spindle drive assembly 108 puts a carefully controlled downforcepressure on the wafer against the belt 178. This pressure can lead to abowing of the belt down between the drive and idle rollers 180,182. Asit is important to present a flat belt surface across the face of thewafer so that the polishing procedure will be uniformly executed, a pairof belt deflection rollers 252 is preferably positioned on the waferreceiving side of the belt 178.

The belt deflection rollers 252, best shown in FIGS. 22, 23 and 25 arepositioned parallel to and between the drive and idle rollers 180,182.The belt deflection rollers project slightly above the plane of thedrive and idle rollers. Preferably the belt deflection rollers deflectthe belt in the range of 0.06-0.13 inches above the plane of the driveand idle rollers. As shown in FIGS. 22 and 25, each belt deflectionroller 252 is affixable to the frame 184 of the polisher 38 by rollersupports 254 that suspend the axle 256 of the roller 252 on either end.

In one preferred embodiment, the roller 252 has a fixed axle 256 and arotatable sleeve 258 mounted on sealed bearings around the axle. Therotatable sleeve 258 is preferably wider than the belt 178. Any of anumber of available roller assemblies capable of supporting severalhundred pounds of distributed pressure may be used as the deflectionrollers 252.

Platen Assembly

Referring again to FIG. 23, the polisher 38 also includes a platenassembly 260. The platen assembly, in conjunction with a platen heightadjuster 262, controls the gap between the back of the belt 178 and theplaten 264. An advantage of the presently preferred platen assembly isthat the platen assembly is capable of making height adjustments withoutthe need to dismantle the entire polisher. The platen assembly 260 canadjust its height during polishing and maintains a very accuratepressure distribution across the wafer. As shown in FIG. 23, the platenassembly 260 is removably attachable to the frame 184 of the polisher 38between the belt deflection rollers 252.

As shown in FIGS. 26-27, the platen assembly 260 comprises a replaceabledisk platen 264 mounted on a disk platen holder 266. A manifold assembly268 underneath the disk platen holder 266 is designed to distributefluid to the disk platen in precise amounts. The disk platen holder 266preferably includes a row of pre-wet nozzles 267 arranged along at leastone of the edges perpendicular to the direction of motion of the belt178. Fluid is directed to the pre-wet nozzles 267 from a pre-wetmanifold 271 on the manifold assembly 268. The pre-wet nozzles reducethe friction of the belt against the edges of the disk platen holder byproviding a small amount of fluid to lubricate the belt as it initiallypasses over the platen assembly 260. Preferably, the fluid utilized isair and the manifold assembly 268 has a plurality of pneumatic quickdisconnect ports 270 that permit easy engagement and disengagement ofair supplies to the platen assembly 260. A platen disk gasket 272provides a seal between the platen 264 and platen holder 266. Similarly,a platen holder gasket 274 supplies a seal between the manifold assembly268 and the platen holder 266. A plurality of fasteners 276 hold theplaten assembly 260 together and four connector holes 278 cooperate withfasteners (not shown) for installing or removing the platen assembly 260from the polisher 38.

In operation, the platen assembly 260 receives a controlled supply ofair, or other fluid, from platen fluid mass flow controllers 280(FIG. 1) positioned on the back end assembly 14 of the system 10. Otherfluid flow control devices may also be used with the presently preferredplaten assembly. The controlled fluid flow from the mass flowcontrollers 280 are received at the manifold assembly 268 anddistributed to the plurality of air distribution vents 282 in the diskplaten 264. The air, or other fluid, emerging from the distributionvents 282 creates a fluid bearing that puts pressure on the belt 178 ina precise, controlled manner while minimizing friction against the beltas it continuously travels over the air bearing. In another preferredembodiment, the manifold assembly may be omitted and individual hoses ortubes may distribute fluid to the appropriate nozzles or vents in theplaten assembly.

Another important aspect of the polisher 38 is a platen height adjuster262 for adjusting the height of the platen 260 with respect to the belt178 as well as for keeping a parallel alignment of the platen 260 withthe belt. The platen height adjust 262 is preferably made up of threeindependently operable lift mechanisms 284. As shown in FIGS. 21 and 23,the lift mechanisms 284 are spaced apart in triangular pattern so thatthe platen assembly 262 can be adjusted to any angle with respect to thebelt 178. The lift mechanisms 284 are positioned between the drive andidle rollers 180, 182 directly beneath the platen assembly 262 in asealed chamber in the frame 184.

FIG. 28 best shows the construction of a preferred lift mechanism 284.Each lift mechanism 284 is driven by a motor 286 controlled by anencoder 288 via a data line 290. The motor 286 drives a planetarygearhead 292 through an adapter 294. The gearhead preferably has a veryhigh gear ratio so that fine adjustments are attainable. One suitablegear ratio is 100:1. A cam mechanism 295 transfers the rotationalmovement of the stepper motor 286 to vertical movement of the liftershaft 296. An annular bearing 298 having male and female sphericalsurfaces (see FIG. 23) provides for multiple degrees of motion to permitthe lift mechanisms 284 on the platen height adjuster 262 to move up anddown without causing excess stress between the platen mounting plate 300and the shafts 296 as the platen is adjusted at the three points ofcontact. The shafts 296 each connect to the mounting plate with a bolt302 and washer 304. A bellows mount 306 and clamp 308 form a sealedjunction with the mounting plate 300 when the platen height adjuster 262is connected to the platen assembly 260 via the mounting plate 300.

Touch-up Polishing Device

A touch-up polisher 40 is mounted below the index table (FIG. 1) andcooperates with the spindle drive assembly 108 mounted in the system 10on the opposite side of the index table 36 to perform a final polishingstep on each wafer proceeding along the process path. The touch-uppolisher used with the wafer polishing system 10 may be any of a numberof known rotary polishing devices, such as those available from EngisCorporation. In one embodiment, the touch-up polishing device 40 may bea linear polishing device, similar to the primary wafer polisher 38described above, adapted to buff a planarized wafer by removing materialfrom the wafer at a rate less than 1,000 (Å/min.).

Another touch-up polisher 40 for use in the wafer polishing system 10 isshown in FIGS. 29-30. This embodiment of the touch-up polisher 40implements a design for simultaneous rotary and linear oscillatingmovement of a polishing plate 330. The polishing plate 330 supports apolishing pad 332 used to remove fine scratches and marks from thesurface of each semiconductor wafer. The pad 332 preferably utilizes apolishing fluid, for example a supply of slurry containingmicroabrasives, to remove material from the wafer at a rate of less than1,000 angstroms per minute. The spindle drive assembly rotates the waferas the wafer is held against the rotating, linearly oscillating touch-uppolisher 40.

The rotary plate 330 connects to a motor 338 via a shaft 336. In oneembodiment, the rotary plate is rotated at a speed of 10-200 revolutionsper minute (r.p.m.) controllable to +/−1 r.p.m. The motor 338, shaft336, and rotary plate 330 are slidably mounted on a linear guideassembly 340 positioned parallel to the surface of the rotary plate 330.The linear guide assembly is affixed to the frame 346 of the touch-uppolisher 40. A linear actuator 344 connected to the linear guideassembly 340 oscillates the mounting plate and attached components sothat the rotary plate 330 moves back and forth in a linear directionalong the linear guide assembly 340 while the rotary plate 330 issimultaneously rotating. The linear actuator 344 is capable ofoscillating the rotary plate and attached components along the linearguide assembly at a rate of 60-600 strokes per minute where a stroke isthe maximum travel in one direction. The stroke may be two inches wherethe linear actuator moves +/−1 inch from a home position along thelinear guide assembly.

The linear actuator may be any type of linear actuator capable oflinearly moving the rotary plate and connected components at apredetermined rate. A rotary polishing mechanism, such as thosemanufactured by Engis Corporation, may be used as the rotary plateportion of the preferred touch-up polisher 40. Although the embodimentof a touch-up polisher shown in FIGS. 29-30 operates to simultaneouslyrotate the rotary plate while oscillating the rotary plate in a lineardirection, the touch-up polisher may be controlled to only move therotary plate in a linear direction without also rotating the rotaryplate. Conversely, a wafer may also be suitably buffed by just rotatingthe rotary plate and not oscillating the rotary plate in a lineardirection.

Control Architecture

FIG. 31 illustrates a preferred communications network and controlarchitecture for managing operation of the wafer polishing system 10.Preferably, the graphic user interface 30 used on the display 28 in thefront end frame assembly 12 allows direct interaction between users andthe cluster tool controller (CTC) 310. The CTC 310 is the main processorfor the system. A suitable cluster tool controller is a compactPCI-based computer running Microsoft NT 4.0. The graphic user interface30 is preferably written using Wonderware In touch tools. A SECS/GEMinterface may be written using GW Associates tools to operate over anRS-232 connection 312 and is used for communications to other equipment.The CTC 310 preferably communicates with process module controllers(PMC) 314 and a transport module controller (TMC) 316 over an ethernetnetwork 318.

Each PMC 314 controls the operation of a wafer processing device (i.e.,the primary polishers 38, touch-up polisher 40, and scrubber assembly32) in accordance with commands from the CTC 310. The PMCs 314 arepreferably compact PCI-based computers running pSOS+ software and arecapable of communicating with the TMC 316 and other PMCs 314 over theethernet network 318.

The TMC 316 is also preferably a compact PCI-based computer runningpSOS+ software. The TMC controls the head loader 34, the dry and wetrobots 20, 24, and the index table 36. The TMC 316 preferably containsscheduling software for insuring that the semiconductor wafers properlyproceed through the system 10.

General Explanation of Process

A preferred method for processing the wafers using the system 10described above is set forth below. Cassettes 16 filled with a pluralityof semiconductor wafers are installed at the front end assembly 12 tobegin the process. The dry robot 20 removes individual wafers and placeseach one on the transfer station 22. The transfer station will align thewafer by rotating the wafer until a characteristic reference mark, forexample a notch or flat, is properly aligned. The wet robot 24 reachesout to the transfer station 22 to remove and flip the wafer so that theside with circuitry, if any, faces down. The wet robot 24 carries thewafer into the back end frame assembly 14 and deposits it on the headloader 34. The head loader then lifts the wafer up to the head assembly52.

The step of transferring the wafer from the head loader to the headassembly is accomplished through synchronized activity at the headloader 34 and the head loader spindle drive assembly 109 positionedabove the head loader. At the head loader, the wet robot has just setthe wafer onto the raised support ring 94. The alignment ring 96 movesup to align the wafer on the support ring 94. The head loader nextraises the tub 90 and moistens the back side of the wafer to assist thehead assembly 52 in gripping the wafer using a vacuum or the surfacetension of the fluid. Because the wafer has previously been flipped, theback side of the wafer is facing up towards the head assembly 52. Thetub 90 is lowered after the moistening is complete. The alignment andsupport rings move up to meet the head assembly and transfer the wafer.

While the back side of the wafer is moistened, the spindle driveassembly moves down to grasp the head assembly. The male and femaleportions of the tool changer on the spindle and head assemblyrespectively are locked together. The head retainer mechanism 68 thenreleases the head assembly 52 from the index table 36. The spindle driveassembly now lowers the head assembly down through the index table tomeet the wafer. The support ring 94 moves the moistened wafer up untilthe suction of air through the air passages 58 on the wafer receivingplate 54 grab the wafer. The head assembly is raised to the index table,locked into the head retainer mechanism and released by the spindle.

The index table rotates the wafer to the first primary wafer polisher 38to begin polishing. As described above, the head assembly holding thewafer is connected to the spindle and brought down to the primary waferpolisher 38. The spindle drive assembly 108 over the primary waferpolisher moves the wafer approximately four inches down from the indextable and, while rotating the wafer at a constant speed, presses thewafer down into the polishing pad on the moving belt 178 with a measureddownforce. The spindle drive assembly 108, platen assembly 260 andplaten height adjuster 262 receive instructions from the process modulecontroller 314 and cooperate to maintain the appropriate pressure andalignment between the wafer and belt. Also, a chemical polishing agent,such as a 10% micro abrasive slurry is continuously or intermittentlyfed onto the polishing pad on the belt and the wafer polishing processis initiated. The wafer is only partly polished, preferably halfpolished, at the first primary polishing device 38. The spindle assemblypulls the wafer back up to the index table after partly polishing thewafer and, after the head assembly is reconnected to the index table andthe spindle detaches, the index table conveys the wafer to the nextprimary wafer polishing device 38. The steps of removing and polishingthe wafer are repeated to complete the polishing of the wafer.

The wafer is reconnected to the index table and moved to the touch-updevice for removal of any scratches or blemishes left from the primarypolishing steps. After buffing in the touch-up polisher, the wafer isagain transported by the index table and returned to the head loader.The head loader executes several steps during the unloading operation.The tub 90 rises up and seals against the index table. Nozzles in thehead loader spray DI water on the face of the wafer. The wafer supportring 94 raises up to the head assembly and the head assembly pushes thewafer off with a gentle burst of gas or liquid. The alignment ring 96raises up around the support ring to align the wafer and then thesupport and alignment rings lower the wafer. With the tub still sealedagainst the index table, the nozzles 100 rinse the back side of thewafer and the wafer retaining portion of the head assembly.

The tub lowers after the rinsing and the wet robot removes the waferfrom the head loader, flips it over and then places the planarized waferinto the scrubber for a final cleaning and drying. The wet robot thenimmediately retrieves an unpolished wafer from the wafer transferstation and places it in the head loader. The dry robot receives thecleaned and dried wafer from the scrubber and places it back into thecassette.

These steps are repeated with each wafer so that all the wafers arehandled by the same devices. All four head receiving areas on the indextable are occupied with wafers when the system is in full operation.After the head loader removes a polished wafer from the head assembly, anew wafer is put on the available head assembly. In a preferredembodiment, each time the index table rotates the head assemblies to anew position over the next processing station, the index table stops andeach spindle drive assembly removes the head assembly (and attachedwafer) positioned below it for processing. All the processing stationsexecute their respective tasks at the same time. An advantage of thepreferred system and method is the improved consistency by processingeach wafer over the same process path to prevent any discrepancies inplanarization between wafers. Also, the system can more efficientlyprocess wafers by breaking up the polishing steps into multiple stepsover two or more polishing devices. Increased throughput is attained byoptimizing the number of polishers 38, 40 along the process path so thata continuous flow of wafers is conveyed along the process path. In theembodiment discussed above, it is assumed that the total time forpolishing is twice as long as the scrubbing and drying steps so twopolishers have been provided and half of the polishing takes place ateach polisher. Thus, the index table can rotate from processing stationto processing station in constant intervals. As can be seen, othermultiples of polishing devices or other processing stations may be useddepending on the limitations of any one processing station or the typeof polishing being performed.

In an alternative embodiment, the presently preferred system may bemodified to execute separate polishing processes along the same processpath. For example, if a wafer is best polished using two or morechemically incompatible polishing processes, the system 10 can beconfigured to isolate each polishing device used along the process pathand rinse the wafer between polishing steps. In another alternativeembodiment, a wet wafer holding area may be added adjacent to the headloader to store processed, wet wafers if the scrubber assembly fails. Inthis way the slurry compounds will remain moist until any problem withthe scrubber is corrected.

From the foregoing an improved system and method for polishingsemiconductor wafers has been described. The method includes the stepsof processing all wafers over a single process path and breaking thepolishing step up over at least two polishers to increase consistencyand throughput. The system includes integrated polishing, buffing andscrubbing devices accessible along a single process path utilizing anindex table conveyor. The system includes a detachable head assembly forexchanging the head assembly between the index table and spindle driveassemblies positioned at each processing station. A head loader isdesigned to load, unload, and rinse wafers moving to and from the indextable. A linear wafer polishing device includes automatic pneumatic belttensioning and steering. Additionally, the polishing device includes apneumatic platen having a manifold that eliminates unnecessary tubing.The platen is movably mounted on a platen height adjuster thataccurately aligns the platen and the belt with the wafer duringpolishing. A spindle drive assembly utilizing two stage verticaladjustment and precise downforce ability is also provided.

It is intended that the foregoing detailed description be regarded asillustrative rather than limiting, and that it be understood that thefollowing claims, including all equivalents, are intended to define thescope of this invention.

We claim:
 1. A wafer polishing station for performing chemicalmechanical planarization of a semiconductor wafer using an abrasivepolishing agent, the wafer polishing station comprising: a polishingmember movable in a linear direction with respect to a surface of thesemiconductor wafer; a polishing member drive assembly for moving thepolishing member in the linear direction having a drive roller and anidle roller, the drive roller rotatably connected to a drive motor; apneumatic steering and tension adjustment mechanism for controllingoperation of the polishing member; and a pair of deflection rollerspositioned under the polishing member and between the drive roller andidle roller, the deflection rollers each having a width greater than awidth of the polishing member.
 2. The wafer polishing station of claim 1further comprising a platen assembly having a fluid manifold connectedto a disk platen, the platen assembly positioned under the polishingmember and between the drive and idle rollers.
 3. The wafer polishingstation of claim 2 wherein the platen assembly is movably mounted on aplaten height adjuster having a plurality of platen lifters.
 4. Thewafer polishing station of claim 3 wherein the disk platen on the platenassembly further comprises a plurality of distribution vents forproviding a fluid received from the fluid manifold to a bottom portionof the polishing member.
 5. The wafer polishing station of claim 4further comprising a plurality of pre-wetting nozzles arranged along atleast one edge of the disk platen assembly perpendicular to a directionof motion of the polishing member, the pre-wetting nozzles receiving afluid from a pre-wetting manifold in the disk platen assembly, wherebythe pre-wetting nozzles provide a fluid to the bottom portion of thepolishing member and help to reduce friction at the edge of the diskplaten assembly.
 6. The wafer polishing station of claim 1 wherein thepneumatic steering and tension adjustment mechanism comprises: first andsecond cylinder assemblies, the cylinder assemblies each having a firstend pivotally attached to an axle of the idle roller on opposite ends ofthe idle roller and the cylinder assemblies each having a second endconnected to a frame of the primary wafer polisher; and a plurality ofsensors electrically connected to the wafer polishing station, the firstand second cylinder assemblies responsive to signals generated by theplurality of sensors to control a tension and alignment of the polishingmember.
 7. The wafer polishing station of claim 6, wherein the pluralityof sensors comprises a load cell positioned on each of the first andsecond cylinder assemblies, the load cells configured to detect atension on the polishing member.
 8. The wafer polishing station of claim7 wherein the plurality of sensors further comprises an alignment sensorpositioned over an edge of the polishing member, the alignment sensorproducing a signal in response to an alignment of the polishing memberon the idle and drive rollers.
 9. The wafer polishing station of claim6, wherein the pneumatic steering and tension adjustment mechanismfurther comprises a pair of slide bars, wherein a first slide bar ispivotally attached at a first end to an end of the axle of the idleroller and attached at a second end to the first cylinder assembly, andwherein the second slide bar is pivotally attached at a first end to anopposite end of the axle of the idle roller and at a second end to thesecond cylinder assembly.
 10. The wafer polishing station of claim 9,wherein the axle of the idle roller includes a slot on each end thatreceives the slide bar and is connected to the slide bar at a rotatablejunction, and wherein a gap between the slot and the slide bar providesa clearance for pivotal movement of the end of the idle axle about therotatable junction.
 11. The wafer polishing station of claim 10, whereinthe rotatable junction is a pin that passes through the slide bar andthe end of the idle axle.
 12. A wafer polishing station for performingchemical mechanical planarization of a semiconductor wafer using anabrasive polishing agent, the wafer polishing station comprising: apolishing member movable in a linear-direction with respect to a surfaceof the semiconductor wafer; a polishing member drive assembly for movingthe polishing member in the linear direction having a drive roller andan idle roller, the drive roller rotatably connected to a drive motor; asteering and tension adjustment mechanism for controlling operation ofthe polishing member; and a pair of deflection rollers positioned underthe polishing member and between the drive roller and idle roller, thedeflection rollers each having a width greater than a width of thepolishing member.
 13. The wafer polishing station of claim 12 furthercomprising a platen assembly having a fluid manifold connected to a diskplaten, the platen assembly positioned under the polishing member andbetween the drive and idle rollers.
 14. The wafer polishing station ofclaim 13 wherein the platen assembly is movably mounted on a platenheight adjuster having a plurality of platen lifters.
 15. The waferpolishing station of claim 14 wherein the disk platen on the platenassembly further comprises a plurality of distribution vents forproviding a fluid received from the fluid manifold to a bottom portionof the polishing member.
 16. The wafer polishing station of claim 15further comprising a plurality of pre-wetting nozzles arranged along atleast one edge of the disk platen assembly perpendicular to a directionof motion of the polishing member, the pre-wetting nozzles receiving afluid from a pre-wetting manifold in the disk platen assembly, wherebythe pre-wetting nozzles provide a fluid to the bottom portion of thepolishing member and help to reduce friction at the edge of the diskplaten assembly.
 17. The wafer polishing station of claim 12, whereinthe steering and tension adjustment mechanism comprises a plurality ofsensors electrically connected to the wafer polishing station, wherebythe plurality of sensors generate signals to control a tension andalignment of the polishing member.
 18. The wafer polishing station ofclaim 17, wherein the plurality of sensors further comprises a loadcell, the load cells configured to detect a tension on the polishingmember.
 19. The wafer polishing station of claim 18 wherein theplurality of sensors further comprises an alignment sensor positionedover an edge of the polishing member, the alignment sensor producing asignal in response to an alignment of the polishing member on the idleand drive rollers.